Recently, solid laser apparatus have been developed which excites a laser medium rod by illumination from a flash lamp, such as a Xenon discharge tube. These apparatus operate such that a condenser is charged by a high direct current voltage applied through a resistor. The voltage charge of the condenser is then discharged all at once by applying a trigger pulse to a flash lamp connected across that condenser.
However, such apparatus have a disadvantage in that the discharge property of the flash lamp, more importantly the pulse waveform of resulting laser light, is fixed by electrical properties peculiar to the flash lamp and by electrical properties peculiar to the discharge property of the condenser, so that the pulse waveform of the resultant laser light is limited to one form.
FIG. 1 illustrates a typical conventional supply device. In FIG. 1 an A.C. input voltage is increased to several KV by an A.C. transformer 1. This increased voltage, after rectifying by a rectifier 2, is supplied to a condenser 4 through a resistor 3. A resultant D.C. high voltage is charged in condenser 4.
The charge voltage of condenser 4 is subsequently supplied between an anode and cathode of a flash lamp (not shown) which is electrically connected across condenser 4. A flash lamp is a kind of discharge tube, and its discharge is carried out only upon issue of a trigger pulse thereto. Thus, the supplied high D.C. voltage continues to charge condenser 4 until discharge occurs upon triggering of the flash lamp.
In such a discharge procedure, the charge voltage of condenser 4 is gradually increased up to a desired voltage value of, for example, several kV as shown in the saturation curve of FIG. 2.
The flash lamp is discharged when a trigger pulse is applied thereto, whereupon the charge voltage of condenser 4 is discharged across the anode and cathode of the flash lamp. Accordingly, the flash lamp immediately emits light to energize a solid laser rod which is disposed in the vicinity of the flash lamp, whereby laser light is generated from the laser rod.
A typical waveform of discharge current of condenser 4 is shown in FIG. 3 to abruptly rise and to slowly descend after reaching a peak value. The peak value of current may be several hundred to several thousand amperes and the discharge time may typically be less than several milliseconds, although those values may vary with supply voltage, kinds of flash lamp or the like.
Generally, the energizing light emitted from a flash lamp is maximized by setting the charge voltage of condenser 4 to a high value, whereby the peak value of laser output is maximized. The laser output value is somewhat changeable by adjustment of the charge voltage level. However, it is difficult to arbitrarily change the pulse width of a laser output because the discharge property of condenser 4 is fixed, as is the performance of the flash lamp itself, as aforementioned.
If the electric charge value of condenser 4 is fixed, the emission light achieved by that electric charge value is also fixed. However, if the light emission is short in time, and the intensity of the light is thereby strong, the laser light generated by that light emission becomes greater. To the contrary, if the light emission time is increased, and the intensity of the light is thereby diluted, the laser light generated by that light emission is reduced.
Since the level of the peak value of laser light corresponds to the level of the instant energy of laser light, even if the total amount of laser light energy per pulse is the same, the higher the peak value is, the higher the instant light energy is. Therefore, in a laser apparatus, if the pulse width of laser output is variable, it is possible to utilize laser light of a variety of peak values, as required.
In the circuit of FIG. 1, since the charging voltage of the condenser is constant and the discharge property is fixed, it is impossible to vary the pulse width of laser output light. However, circuits as shown in FIGS. 4 and 5, do operate to change the pulse width by discharging a plurality of condensers with sequential delay times using delay circuits.
These delay circuits utilize either a ladder-type circuit of FIG. 4 construction with inductances 41, 42, and 43, and capacitances 44, 45, and 46, or a ladder-type circuit of FIG. 5 construction with resistances 51, 52, and 53, and capacitances 54, 5, and 56. A D.C. high voltage is applied between input terminals 50a and 50b of such circuits to charge the capacitances. A flash lamp is connected between output terminals 57a and 57b.
Subsequently, upon applying a trigger to the flash lamp, in the case of FIG. 4, the charge of capacitance 46 nearest to the output terminals 57a and 57b is first discharged to flow into the flash lamp. At this time, although the charge of the second capacitance 45 is also urged to discharge, its discharge is restrained by function of the inductances 42 and 43. Discharge of capacitance 45 is instead started with a delay determined by a time constant which is a function of the component values. The second capacitance 45 and first capacitance 44 subsequently discharge at times delayed from the discharge starting time of capacitance 46, whereby the total discharge time is lengthened and the pulse width of discharge current flowing to the flash lamp is increased.
The operation of the circuit shown in FIG. 5 is similar. The discharge of capacitance 56 is carried out first. The discharge of capacitance 55 is delayed from the discharge of capacitance 56 by a time constant which is determined by the relation of resistances 53 and 52. The discharge of capacitance 54 is similarly delayed, so that the total discharge time is long and, accordingly, the pulse width of the laser output is long.
It is thus possible to control the pulse width to a desired value by selecting the values of inductances 41, 42, and 43 (FIG. 4) or resistances 51, 52, and 53 (FIG. 5).
However, in the circuit of FIG. 4, a large current of hundreds to thousands of amperes flows, so that the current capacity of inductances 41, 42, and 43 must be large. This results in large problems regarding the volume and weight of inductances 41, 42, and 43. Furthermore, in order to increase the current capacities of inductances 41, 42, and 43, the inductances 41, 42, and 43, should be made of a hollow core type. Consequently, in order to obtain sufficient inductance capacity, winding turns must be great, inviting large size and high cost.
In the case of the circuit of FIG. 5, since current as large as hundreds to thousands of amperes flows in resistances 51, 52, and 53, these resistances must have large current capacities. Therefore, the resulting device is large as well as expensive and energy loss is great due to such resistance, resulting in decreased efficiency.
It is, therefore, an object of this invention to provide a power source apparatus for a flash lamp used in a pulse laser apparatus which can supply a variable width pulse of current to a flash lamp without energy loss.
More specifically, it is an object of the invention to provide a compact, inexpensive power source apparatus for a flash lamp used in a pulse laser apparatus.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particular pointed out in the appended claims.